As one type of magnetic resistive memory, there is a magnetoresistive random access memory (MRAM). The magnetoresistive random access memory is a memory that stores data by utilizing the fact that a resistance value of a magnetoresistive effect element changes owing to a change in relative relationship in the magnetizing directions of two ferromagnetic layers of the magnetoresistive effect element.
A memory cell in the magnetoresistive random access memory has a magnetoresistive effect element in which a plurality of ferromagnetic layers and a nonmagnetic layer are laminated, and a field-effect transistor that functions as a selecting switch (which will be referred to as a select transistor hereinafter). The magnetoresistive effect element includes a ferromagnetic layer having an invariable magnetizing direction (which will be referred to as a magnetization invariable layer or a reference layer hereinafter), a ferromagnetic layer having a variable magnetizing direction (which will be referred to as a magnetization free layer or a storage layer hereinafter), and a nonmagnetic layer sandwiched between these ferromagnetic layers. Thus, data is written by changing the magnetizing direction of the magnetization free layer.
In general, the select transistor is arranged on a semiconductor substrate, and the magnetoresistive effect element is arranged in an interconnect level above the select transistor through an interlayer insulating film. To connect the select transistor with the magnetoresistive effect element, a contact plug buried in the interlayer insulating film is used.
For example, the magnetoresistive effect element is arranged immediately above the contact plug through a lower electrode. A crystal structure of a metal of the contact plug is usually different from a crystal structure of a magnetic layer. Therefore, when the lower electrode cannot buffer a difference in crystal structure between the contact plug and the magnetic layer, there is a concern that crystallinity of the contact plug affects crystallinity of the magnetic layer. Characteristics of the magnetoresistive effect element are largely dependent on the crystallinity of the magnetic layer of the element. Therefore, when the crystallinity of the magnetic layer is affected by the crystallinity of the contact plug, element characteristics are degraded.
Further, as a method of avoiding adverse affect of the crystallinity of the contact plug with respect to the magnetoresistive effect element, the magnetoresistive effect element may be shifted in a parallel direction from a position immediately above the contact plug for the rearrangement of the element in some cases (see, e.g., JP-A 2005-44848 (KOKAI)). In this case, a step of processing the magnetoresistive effect element and a step of processing the lower electrode by using a photolithography technology and an etching technology are separately executed, with the result that the number of manufacturing steps increases and a manufacturing cost accordingly increases.